The present invention relates to a method and apparatus for dispensing a setable material, such as bone cement. More particularly, it relates to a method and apparatus consisting of two syringes having their nozzles or dispensing ports interconnected so that material may be transferred back and forth from one syringe to the other.
Bone fillers and cements are widely used in dental, maxio-facial and orthopedic applications. Such cements are made by mixing a liquid and powdered component to form a paste which then sets to form a hard cement or filler.
Such a cement using calcium phosphate is described by Brown and Chow in their reissued U.S. Pat. Nos. RE 33,161 and RE 33,221 and by Constantz et al. in their U.S. Pat. No. 5,820,632. Such a cement using polymethyl methacrylate is described in U.S. Pat. Nos. 4,900,546 and 5,276,070. Mixing devices for these powder and liquid components have been the subject of numerous patents.
The use of two syringes to mix two liquid substances and then dispense the mixture from one syringe is known from U.S. Pat. No. 3,700,215 to Hardman et al. This patent illustrates the outlet nozzles of a pair of syringes connected by a coupling. A perforated mixing tube is slidably mounted within the coupling so that depressing the plunger on one syringe drives the liquid contents of that syringe through the tube into the other syringe and simultaneously drives the perforated mixing tube into the other syringe. The plunger of the other syringe is then depressed, causing the contents to be driven back into the first syringe. This process is repeated a desired number of times until the liquid substances are appropriately mixed. This mixing system is unsuitable for transferring an only partially wetted powdered and liquid component from one syringe to another.
U.S. Pat. No. 4,743,229 to Chu illustrates a pair of syringes coupled at their outlet nozzles. One of the syringes contains a fibrillar collagen which is injected into the second syringe which contains particulate mineral material. No further mixing is taught.
U.S. Pat. No. 5,908,054 to Safabash et al. relates to a pair of syringes coupled by a fluid transfer assembly. A hollow tube is mounted within the syringes and has first and second ends situated within the interiors of the syringes. The tube has openings to permit the flow of fluid to be transferred from the interior of the first syringe to the second syringe. Again, this design is unsuitable for passing a high viscosity partially mixed granular/liquid material through the tube.
U.S. Pat. No. 5,957,166 to Safabash relates to a device similar to that shown in his U.S. Pat. No. 5,908,054, with the exception that the perforated tube has a pattern of holes wherein the size and spacing is adjusted to provide an uneven fluid distribution within the second syringe. Again, such a device is unsuitable for transferring a viscous mixture from one syringe to another syringe.
U.S. Pat. No. 4,551,135 to Gorman et al. relates to a two component mixing syringe having a flared barrel to facilitate to the extrusion of the plastasized mass. U.S. Pat. No. 4,046,145 discloses a connector for use in connecting a pair of syringes.
None of the above references disclose a mechanism designed to allow a syringe containing a liquid component to be connected to a syringe containing a powdered component and allowing the liquid to be injected into the powder in the second syringe and then enabling the liquid-powder combination to be injected back into the first syringe. It has been found that the initial injection of the liquid-powder combination back into the first syringe can require more force than can be generated by simply manually depressing the plunger of the second syringe. Consequently, a mechanism has been provided to assist the individual mixing the liquid and powder components in moving the materials back and forth from one syringe to the other over a number of cycles. It has also been found that imparting mechanical energy into the mixture during mixing beyond that inputted by hand mixing increases the final strength of the set material. This is accomplished by repeating the transfer from syringe to syringe for several cycles after wetting.
A primary object of the present invention is to provide a simple and inexpensive mixing and dispensing device which will enable the mixing of a setable powder and liquid combination by assisting in the movement of the liquid stored in a first syringe into a powdered component stored in a second syringe and then moving the combination back to the first syringe and repeating the transfer over a number of cycles.
It is a further object of the invention to provide a kit containing two syringes, one containing a liquid component and the other containing a powder component which, when mixed, form a setable cement for use in filling bone defects and inducing bone healing.
It is another object of the invention to enable the end to end connection of two syringes and allowing the connected syringes to be placed in a simple mechanism which allows for the mixing of the liquid and powdered components by the repeated transfer of the liquid powder combination from one syringe to the other.
It is yet an additional object of the invention to move the mixed cement into one syringe, dissembling the two syringes and using the syringe filled with the mixed liquid and powdered components as a dispensing syringe for placing the mixed cement prior to its setting in vivo where it sets to form hard bone cement or bone filler.
These and other objects of the invention are accomplished by an apparatus for mixing a liquid component and a powdered component which includes first and second syringes, each having a barrel with an exit port at a first end and plunger moveable within the barrel along a longitudinal axis of said barrel. Activation of an outer portion of the plunger which extends beyond a second end of the barrel opposite the first end causes the plunger tip to move towards the exit port or nozzle. The first syringe contains a liquid component and the second syringe contains a powdered component. A mechanism for mixing the two components has a part operatively connected to each of the barrels and a part connected to the portion of the plunger on each syringe extending beyond the end of the barrel so that the relative sliding movement of the two mechanism parts simultaneously moves the plungers and the barrels with respect to each other.
The first part of the mechanism has contact surfaces for contacting the outer portion of the plungers extending beyond the end of each barrel and the second part contacts each barrel portion and supports the same. The first and second parts are slidably moveable with respect to one another in a direction parallel to the longitudinal axis of each barrel. Each barrel has a flange located at a predetermined distance along its length and extending from an outer surface of the barrel for contacting the second part of this mechanism in a manner which prevents axial movement of the barrel with respect to the second part. Likewise, the outer portion of the plungers are captured within the first part of the slide mechanism to prevent relative movement of the plungers with respect to the first part. To mix the cement, the second part slides with respect to the first part of the mechanism such that the plungers remain stationary with respect to the first part with the barrels being moved by the second part relative to the plungers held by the first part. A handle is provided on one of the first or second parts to enable the individual doing the mixing to generate sufficient force to move the combined liquid and powder components from one syringe to the other.
The first and second parts slide with respect to each other a distance equal to the initial distance between a tip of said plunger facing the exit port and the exit port so that the entire contents of each syringe are transferred from one syringe to the other during each cycle of mixing. In general, once all of the powder component has been wetted by the liquid component, three to five cycles of mixing have been found sufficient to completely mix the cement to a homogenous consistency.
The method for mixing the two component cement includes placing a liquid component in the barrel of a first syringe where the syringe has a moveable plunger and an exit port, both extending along a longitudinal axis of the barrel. Placing a powdered component in the barrel of a second syringe with the syringe again having a moveable plunger and an exit port both extending along a longitudinal axis of the barrel. Then connecting both exit ports of each syringe and transferring the liquid component of the first syringe of the second syringe by activating the plunger of the first syringe. Thereafter, the combined liquid and powdered components are transferred from the second syringe back to the first syringe by activating the plunger in the second syringe and repeating the back and forth transfer between the first syringe and the second syringe until the powder is completely wetted and then at least two additional times and preferably three to five. The syringes are then dissembled with the syringe containing the combined liquid and powdered component being using to dispense the mixture into the body.
While the preferred method of mixing is manual, those skilled in the art could easily develop a powered reciprocating mechanism for simultaneously moving the plungers back and forth within the barrels of the syringes.